This invention relates to the guidance of self-propelled sprinkler mobile irrigation systems and, particularly, to a guidance system in which each wheeled support unit along the length of a long irrigation pipe is held in alignment by a laser plane projected from a movable source and sensed by motor-actuating detectors on the wheeled support units whenever the irrigation pipe becomes misaligned.
In recent years there have been many advances in the development of large self-propelled sprinkler irrigation systems. The improved systems have proved to be very much more efficient in speed, labor requirements, and water consumption than were the older flood-type irrigation systems. In general, such sprinkler systems pump the irrigation water from a central well or other water source into a long supply pipe that carries rotating sprinklers at appropriate intervals and which is supported along its length by a pluality of spaced movable carriages that very slowly pivot the pipe around the irrigation water source. In areas where there are very large and relatively flat tracts, the systems are often over a quarter of a mile in length and provide efficient irrigation to huge farm tracts.
Self-propelled sprinkler irrigation systems employing multiple pipe supporting carriages must incorporate some means for independently controlling movement of the carriages to assure that the water supply pipe is maintained reasonably straight while it is slowly, and sometimes intermittently, moving. Most often, this is accomplished by a system of control cables that are rigged along the supply pipe so that they are subjected to stress changes as the pipe bends. These stress changes may then be translated into motion that may be used to control drive motors that are electrically driven or powered by the water flow in the pipe, or control actuating pistons coupled to linkage that will adjust the location of the pipe carriage to the point of neutral stress of the control cables.
The central well system described above irrigates a large circular pattern and, in the typical square farm tract, fails to cover over 20% of the tract, or approximately 34 unproductive acres per quarter section. While such inefficiency may have been considered negligible during times and in areas where land costs were relatively low and crops were abundant, rising land costs demand that full use be made of all tillable soil. Therefore, the practical irrigation system of today is one that will evenly irrigate a full rectangular pattern. This, of course, may be accomplished by replacing the central pivot of the above-described systems with an irrigating water source that moves linearly, such as by the use of a carriage supported system that pumps irrigation water into the supply pipe as the carriage moves along an irrigation canel that runs the length of the farm tract. Such a system is described, for example, in U.S. Pat. No. 2,628,863, now expired. It has been found, however, that the self-propelled irrigation systems that employ the above-described stressed control cable system of pipe alignment do not track adequately to accommodate rectilinear pipe movement over long rectangular areas. Efforts to so use the control cable systems have resulted in damage to the pipe and its supporting structure and in unsatisfactory irrigation with some areas receiving excessive or inadequate quantities of water because of excessive pipe bending during the irrigating process.